# US 9,304,410 B2 · Apparatus and method of direct writing with photons beyond the diffraction limit

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- Number: US 9,304,410 B2
- Document ID: US9304410B2
- Status: Granted
- Kind: B2
- Application number: 14/143,139
- Filed: 2013-12-30
- Published: 2015-11-19
- Granted: 2016-04-05
- Earliest claimed: 2011-11-18
- Assignees: Periodic Structures, Inc.
- Applicants: David A. Markle; Rudolf H. Hendel; John S. Petersen; Hwan J. Jeong
- Inventors: David A. Markle; Rudolf H. Hendel; John S. Petersen; Hwan J. Jeong
- Web page: https://patentgrep.com/patent/US9304410B2

## CPC

- G03F 7/7045: {Hybrid exposures, i.e. multiple exposures of the same area using different types of exposure apparatus, e.g. combining projection, proximity, direct write, interferometric, UV, x-ray or particle beam}
- G03F 7/70191: {Optical correction elements, filters or phase plates for controlling intensity, wavelength, polarisation, phase or the like}
- G03F 7/70291: {Addressable masks, e.g. spatial light modulators [SLMs], digital micro-mirror devices [DMDs] or liquid crystal display [LCD] patterning devices}
- G03F 7/70375: {Multiphoton lithography or multiphoton photopolymerization; Imaging systems comprising means for converting one type of radiation into another type of radiation}
- G03F 7/70383: {Direct write, i.e. pattern is written directly without the use of a mask by one or multiple beams (maskless lithography using a programmable mask G03F7/70291)}
- G03F 7/70408: {Interferometric lithography; Holographic lithography; Self-imaging lithography, e.g. utilizing the Talbot effect}
- G03F 7/70466: {Multiple exposures, e.g. combination of fine and coarse exposures, double patterning or multiple exposures for printing a single feature (stitching G03F7/70475)}
- G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G)

## Abstract

Direct-write lithography apparatus and methods are disclosed in which a transducer image and an image of crossed interference fringe patterns are superimposed on a photoresist layer supported by a substrate. The transducer image has an exposure wavelength and contains bright spots, each corresponding to an activated pixel. The interference image has an inhibition wavelength and contains dark spots where the null points in the crossed interference fringes coincide. The dark spots are aligned with and trim the peripheries of the corresponding bright spot to form sub-resolution photoresist pixels having a size smaller than would be formed in the absence of the dark spots.

## Claims

### Claim 1

A direct-write lithography apparatus for printing sub-resolution pixels in a photoresist layer on a substrate, comprising:
a movable stage system configured to movably supports the substrate;
an illumination system configured to provide illumination light of an exposure wavelength capable of activating the photoresist;
at least one image transducer having an array of configurable transducer pixels arranged to receive and selectively modulate the illumination light;
an objective lens arranged to receive the modulated illumination light from the at least one image transducer and form on the photoresist layer a transducer image having an arrangement of bright spots;
an interference pattern generator arranged relative to the objective lens and adapted to generate light beams of an inhibition wavelength capable of inhibiting the activation of the photoresist, wherein the objective lens is configured to receive the light beams to form therefrom on the photoresist an interference image having a grid pattern that defines an array of dark spots, wherein the bright spots are larger than the dark spots, and wherein the transducer image is formed after or simultaneously with the interference image; and
wherein the stage system and the interference pattern generator are configured to respectively move the substrate and the interference image in synchrony relative to the transducer image to expose the photoresist, with the dark spots traversing at least a portion of corresponding ones of the bright spots so that each first dark spot trims a periphery of the corresponding first bright spot without smearing to form the sub-resolution pixels in the photoresist.

### Claim 2 (depends on 1)

The direct-write lithography apparatus of claim 1, wherein the interference pattern generator includes a plurality of fringe shifters configured to shift the grid pattern of the interference image to move the dark spots with respect to the bright spots of the transducer image.

### Claim 3 (depends on 2)

The direct-write lithography apparatus of claim 2, wherein the fringe shifters having a servo-bandwidth of 40 kHz or greater.

### Claim 4 (depends on 1)

The direct-write lithography apparatus of claim 1, where the configurable transducer pixels are arrayed like white squares on a checkerboard.

### Claim 5 (depends on 1)

The direct-write lithography apparatus of claim 1, wherein the substrate includes an alignment mark, and wherein the apparatus further comprises:
a camera unit arranged to view the substrate through the objective lens to capture an image of the transducer image and the interference image as formed on the substrate; and
an alignment system operably coupled to the camera unit and the stage system, the alignment system configured to measure relative positions of the superimposed transducer and interference images and the alignment mark.

### Claim 6 (depends on 1)

The direct-write lithography apparatus of claim 1, wherein the exposure wavelength is nominally 405 nm and the inhibition wavelength is nominally 532 nm.

### Claim 7 (depends on 1)

The direct-write lithography apparatus of claim 1, wherein the substrate has an area and wherein the movable stage system is configured to scan the substrate back and forth at a constant velocity under the objective lens during the exposure and between exposures to expose substantially all of the substrate area.

### Claim 8 (depends on 1)

The direct-write lithography apparatus of claim 1, wherein the sub-resolution pixels formed in the photoresist have a size in the range from 5 nm to 100 nm.

### Claim 9 (depends on 1)

The direct-write lithography apparatus of claim 1, wherein the transducer pixels are defined by micro-mirrors that have first and second states, and wherein in the first state the micro-mirrors are irradiated with illumination light from a first direction and in the second state are irradiated with inhibition light from a second direction, wherein the exposure light and the inhibition light are directed through the objective lens to the photoresist layer.

### Claim 10

An apparatus for performing direct-write lithography in a photoresist layer supported by a substrate, comprising:
means for forming on the photoresist layer two or three interference fringe patterns oriented symmetrically about an axis normal to the photoresist resist layer and having an inhibition wavelength that acts on the photoresist layer to inhibit exposure of the photoresist by an exposure wavelength different from the inhibition wavelength, wherein the interference fringe patterns form an interference image that defines an array of dark spots;
means for superimposing on the interference image an image of a transducer having an array of transducer pixels with a select orientation that matches that of the dark spots, the transducer image having the exposure wavelength and comprising an array of bright spots that are images of activated transducer pixels in the array of transducer pixels, wherein the transducer image is formed after or simultaneously with the interference image, and wherein the bright spots are larger than the dark spots; and
means for moving the interference image and the substrate in synchrony while flash exposing the transducer image to scan the dark spots across the bright spots during each flash exposure, wherein each bright spot is trimmed by the corresponding dark spot to form a sub-resolution photoresist pixel having a size smaller than if the dark spot were absent.

### Claim 11

An apparatus for performing direct-write lithography in a photoresist layer supported by a substrate to form sub-resolution photoresist pixels, comprising:
a movable stage system that movably support the substrate;
an objective lens arranged adjacent the substrate;
an illuminator system configured to generate flashes of illumination light;
an interference pattern generator arranged relative to the objective lens opposite the substrate and that generates in combination with the objective lens at least two movable interference fringe patterns at the photoresist layer, the at least two interference fringe patterns having an inhibition wavelength that acts on the photoresist layer to inhibit exposure of the photoresist at an exposure wavelength different from the inhibition wavelength, the at least two interference fringe patterns defining a movable interference image having an array of dark spots;
an image transducer having an array of configurable transducer pixels arranged to receive and selectively modulate the illumination light incident thereon from the illuminator system and to form in combination with the objective lens a transducer image at the photoresist layer, the transducer image having the exposure wavelength and comprising an array of bright spots that are larger than the dark spots of the interference image, wherein the transducer image is formed after or simultaneously with the interference image; and
wherein the movable stage system and the interference pattern generator respectively cause the substrate and interference image to move in synchrony while the illuminator system illuminates the transducer with the flashes of illumination light to effectuate scanning of the dark spots relative to the bright spots to expose the photoresist layer to form the sub-resolution photoresist pixels in the photoresist without smearing.

### Claim 12 (depends on 11)

The direct-write lithography apparatus of claim 11, wherein the interference pattern generator includes a plurality of fringe shifters configured to shift the at least two movable interference fringe patterns of the interference image to move the dark spots with respect to the bright spots.

### Claim 13 (depends on 12)

The direct-write lithography apparatus of claim 12, wherein the fringe shifters having a servo-bandwidth of 40 kHz or greater.

### Claim 14 (depends on 11)

The direct-write lithography apparatus of claim 11, wherein the substrate includes an alignment mark, and wherein the apparatus further comprises:
a camera unit arranged to view the substrate through the objective lens to capture an image of the transducer image and the interference image as formed on the substrate; and
an alignment system operably coupled to the camera unit and the stage system, the alignment system configured to measure relative positions of the superimposed transducer and interference images and the alignment mark.

### Claim 15 (depends on 11)

The direct-write lithography apparatus of claim 11, wherein the exposure wavelength is nominally 405 nm and the inhibition wavelength is nominally 532 nm.

### Claim 16 (depends on 11)

The direct-write lithography apparatus of claim 11, wherein the substrate has an area and wherein movable stage system is configured to scan the substrate back and forth at a constant velocity under the objective lens during the exposure and between exposures to expose substantially all of the substrate area.

### Claim 17 (depends on 11)

The direct-write lithography apparatus of claim 11, wherein the sub-resolution photoresist pixels have a size in the range from 5 nm to 100 nm.

### Claim 18 (depends on 11)

The direct-write lithography apparatus of claim 11, wherein the transducer pixels are defined by micro-mirrors that have first and second states, and wherein in the first state the micro-mirrors are irradiated with illumination light from a first direction and in the second state are irradiated with inhibition light from a second direction, wherein the exposure and inhibition light is directed through the objective lens to the photoresist layer.

### Claim 19 (depends on 11)

The direct-write lithography apparatus of claim 11, wherein the objective lens forms a demagnified transducer image.

### Claim 20 (depends on 11)

The direct-write lithography apparatus of claim 11, wherein the photoresist has a threshold exposure dose, and wherein each bright spot has an exposure dose that is within a value of 1.333 and 1.82 of the threshold exposure dose.